1. Field of the Invention
The present invention relates to novel treatments of porous webs. The treatments impart specific functional properties to the porous web, yet provide for the retention of such desirable properties as porosity, breathability, and tactile feel. The present invention more particularly relates to methods to controllably and selectively place one or more modifiers and a curable, shear thinning, polymer composition into a web. The controlled placement of modifiers is accomplished by the introduction of sufficient energy to controllably and selectively place said modifier(s) and curable, shear thinning, polymer composition into said web. Controlled placement is preferably performed through the manipulation of chemical and physical properties inherent in the modifiers, and the energy controlled viscosity and rheology modified placement of the polymer composition. Selective placement of modifiers is typically accomplished by 1) optionally pre-treating a web with one or more modifiers through saturation methods known in the art; 2) optionally mixing one or more modifiers with a polymer composition; 3) applying the optionally mixed polymer composition onto a surface of the web; 4) shear thinning the composition and placing it into the web; 5) optionally applying one or more modifiers to the surface of the treated web and forcing the modifier(s) into the web and polymer composition; and 6) curing the polymer composition. This method produces a web having modifiers oriented on and within: (a) a thin film of a polymer composition encapsulating the structural elements (i.e., the fibers or filaments) making up the web, leaving at least some of the interstitial spaces open; (b) an internal layer of a polymer composition between the upper and lower surfaces of the web; or (c) some combination of the foregoing.
2. Description of Related Art
In the prior art it has been proposed to treat porous webs, especially fabrics, with silicone resins and also with fluorochemicals. Conventional treatments of webs fall into the general categories of (i) surface coatings and (ii) saturations or impregnations.
For example, U.S. Pat. Nos. 3,436,366; 3,639,155; 4,472,470; 4,500,584; and 4,666,765 disclose silicone coated fabrics. Silicone coatings are known to exhibit relative inertness to extreme temperatures of both heat and cold and to be relatively resistant to ozone and ultraviolet light. Also, a silicone coating can selectively exhibit strength enhancement, flame retardancy and/or resistance to soiling. Fluorochemical treatment of webs is known to impart properties, such as water repellency, soil resistance, grease resistance, and the like.
Prior art fluorochemical and silicone fabric treatment evidently can protect only that side of the fabric upon which they are disposed. Such treatments significantly alter the hand, or tactile feel, of the treated side. Prior silicone fabric coatings typically degrade the tactile finish, or hand, of the fabric and give the coated fabric side a rubberized finish which is not appealing for many fabric uses, particularly garments.
U.S. Pat. No. 4,454,191 describes a waterproof and moisture-conducting fabric coated with a hydrophilic polymer. The polymer is a compressed foam of an acrylic resin modified with polyvinyl chloride or polyurethane and serves as a sort of "sponge", soaking up excess moisture vapor. Other microporous polymeric coatings have been used in prior art attempts to make a garment breathable, yet waterproof.
Various polyorganosiloxane compositions are taught in the prior art that can be used for making coatings that impart water-repellency to fabrics. Typical of such teachings is the process described in U.S. Pat. No. 4,370,365 which describes a water repellent agent comprising, in addition to an organohydrogenpolysiloxane, either one or a combination of linear organopolysiloxanes containing alkene groups, and a resinous organopolysiloxane containing tetrafunctional and monofunctional siloxane units. The resultant mixture is catalyzed for curing and dispersed into an aqueous emulsion. The fabric is dipped in the emulsion and heated. The resultant product is said to have a good "hand" and to possess waterproofness.
This type of treatment for rendering fabrics water repellent without affecting their "feel" is common and well known in the art. However, it has not been shown that polyorganosiloxanes have been coated on fabrics in such a way that both high levels of resistance to water by the fibers/filaments and high levels of permeability to water vapor are achieved. As used herein, the term "high levels of permeability to water vapor" has reference to a value of at least about 500 gms/m.sup.2 /day, as measured by ASTM E96-80B. Also, as used herein, the term "high level of waterproofness" is defmed by selective testing methodologies discussed later in this specification. These methodologies particularly deal with water resistance of fabrics and their component fibers.
Porous webs have been further shown to be surface coated in, for example, U.S. Pat. Nos. 4,478,895; 4,112,179; 4,297,265; 2,893,962; 4,504,549; 3,360,394; 4,293,611; 4,472,470; and 4,666,765. These surface coatings impart various characteristics to the surface of a web, but do not substantially impregnate the web fibers. Such coatings remain on the surface and do not provide a film over the individual internal fibers and/or yarn bundles of the web. In addition, such coatings on the web surface tend to wash away quickly.
Prior art treatments of webs by saturation or impregnation also suffer from limitations. Saturation, such as accomplished by padbath immersion, or the like, is capable of producing variable concentrations of a given saturant chemical.
To treat a flexible web, by heavy saturation or impregnation with a polymer material, such as a silicone resin, the prior art has suggested immersion of the flexible web, or fabric, in a padbath, or the like, using a low viscosity liquid silicone resin so that the low viscosity liquid can flow readily into, and be adsorbed or absorbed therewithin. The silicone resin treated product is typically a rubberized web, or fabric, that is very heavily impregnated with silicone. Such a treated web is substantially devoid of its original tactile and visual properties, and instead has the characteristic rubbery properties of a cured silicone polymer.
U.S. Pat. No. 2,673,823 teaches impregnating a polymer into the interstices of a fabric and thus fully filling the interstices. This patent provides no control of the saturation of the fabric. It teaches full saturation of the interstices of the fabric.
The prior art application of liquid or paste compositions to textiles for purposes of saturation and/or impregnation is typically accomplished by an immersion process. Particularly for flexible webs, including fabric, an immersion application of a liquid or paste composition to the web is achieved, for example, by the so-called padding process wherein a fabric material is passed first through a bath and subsequently through squeeze rollers in the process sometimes called single-dip, single-nip padding. Alternatively, for example, the fabric can be passed between squeeze rollers, the bottom one of which carries the liquid or paste composition in a process sometimes called double-dip or double-nip padding.
Prior art treatment of webs that force a composition into the spaces of the web while maintaining some breathability have relied on using low viscosity compositions or solvents to aid in the flow of the composition. U.S. Pat. No. 3,594,213 describes a process for impregnating or coating fabrics with liquified compositions to create a breathable fabric. This patent imparts no energy into the composition to liquify it while forcing it into the spaces of the web. The composition is substantially liquified before placement onto and into the web. U.S. Pat. No. 4,588,614 teaches a method for incorporating an active agent into a porous substrate. This patent utilizes a solvent to aid in the incorporation of the active agent into the web. The active agent is a non-curable agent since the addition of heat aids in the reduction of viscosity.
One prior art silicone resin composition is taught by U.S. Pat. Nos. 4,472,470 and 4,500,584, and includes a vinyl terminated polysiloxane, typically one having a viscosity of up to about 2,000,000 centipoises at 25.degree. C., and a resinous organosiloxane polymer. The composition further includes a platinum catalyst, and an organohydrogenpolysiloxane crosslinking agent, and is typically liquid. Such composition is curable at temperatures ranging from room temperature to 100.degree. C. or higher depending upon such variables as the amount of platinum catalyst present in the composition, and the time and the temperature allowed for curing.
Such compositions may additionally include fillers, including finely divided inorganic fillers. Silicone resin compositions that are free of any fillers are generally transparent or translucent, whereas silicone resin compositions containing fillers are translucent or opaque depending upon the particular filler employed. Cured silicone resin compositions are variously more resinous, or hard, dependent upon such variables as the ratio of resinous copolymer to vinyl terminated polysiloxane, the viscosity of the polysiloxane, and the like.
Curing (including polymerization and controlled crosslinking) can encompass the same reactions. However, in the fabric finishing arts, such terms can be used to identify different phenomena. Thus, controllable and controlled curing, which is taught by the prior art, may not be the same as control of crosslinking. In the fabric finishing arts, curing is a process by which resins or plastics are set in or on textile materials, usually by heating. Controlled crosslinking may be considered to be a separate chemical reaction from curing in the fabric finishing arts. Controlled crosslinking can occur between substances that are already cured. Controlled crosslinking can stabilize fibers, such as cellulosic fibers through chemical reaction with certain compounds applied thereto. Controlled crosslinking can improve mechanical factors such as wrinkle performance and can significantly improve and control the hand and drape of the web. Polymerization can refer to polymer formation or polymer growth.
Prior art fabrics that exhibit functional properties such as antimicrobial activity, blood repellency, electrical conductivity, fire resistance, and the like, rely on surface coatings or layers of materials to achieve the desired result. Prior art references describe articles having improved performance and functional properties at the expense of comfort and breathability. Greater comfort sacrifices maximum functionality and greater functionality sacrifices comfort.
U.S. Pat. Nos. 4,872,220; 5,024,594; 5,180,585; 5,335,372; and 5,391,423; describe articles that use layers of fabrics and/or polymers to protect against blood, microbes, and viruses from penetrating through the fabrics. U.S. Pat. No. 4,991,232 describes a medical garment comprising a plurality of plies to prevent blood from penetrating through the garment.
Other prior art articles create "zones" upon a thin film surface to impart specific functional properties. For example, U.S. Pat. No. 5,110,683 comprises a semimetallic zone and an electrically insulating zone superimposed on one another. U.S. Pat. No. 5,085,939 describes a thin film-coated polymer web comprising a thin film electronic device on the surface of the thin film. U.S. Pat. No. 4,961,985 describes a coating with specific functional properties attached to the coating.
Accordingly, what is needed in the art are porous articles having improved performance and functional properties, as well as methods for the preparation thereof, while maintaining breathability and hand.